SIRT3 Deacetylates TFAM to Promote Mitochondrial Biogenesis

SIRT3 is a NAD+-dependent mitochondrial protein deacetylase participating in the regulation of central metabolism and mitochondrial proteostasis. SIRT3 is downregulated in clear cell renal cell carcinoma (ccRCC), a main type of renal cancers, but the function of SIRT3 in tumorigenesis and development of ccRCC remains unknown. In this study, we established a SIRT3 overexpressed cell line to explore the changes of proteomics and metabolomics regulated by SIRT3 expression. Both the results of quantitative proteomics, metabolomics and acetylome showed overexpression of SIRT3 increased mitochondrial biogenesis and reversed the mitochondrial dysfunctions in ccRCC. We found SIRT3 could increase the activity of TFAM through modulation of TFAM transcription, degradation and acetylation level. The acetylation of TFAM K154 decreased while TFAM protein expression increased after SIRT3 overexpression. Further study revealed that SIRT3 could bind with TFAM, and decrease the acetylation of TFAM, promoting TFAM activity in mitochondrial biogenesis. Overall, our results present a new mechanism of SIRT3 in regulating mitochondrial functions, and the downregulation of SIRT3 in ccRCC lowers the activity of TFAM, subsequently inhibits the transcription of mitochondrial genes and mitochondrial biogenesis.

SIRT3是一种烟酰胺腺嘌呤二核苷酸（NAD+）依赖的线粒体蛋白去乙酰化酶，参与中枢代谢与线粒体蛋白质稳态的调控。SIRT3在透明细胞肾细胞癌（clear cell renal cell carcinoma, ccRCC，肾癌的主要病理类型）中表达下调，但SIRT3在ccRCC发生发展中的功能仍有待阐明。本研究构建了SIRT3过表达细胞系，以探究SIRT3表达调控的蛋白质组学与代谢组学变化。定量蛋白质组学、代谢组学及乙酰化修饰组学的结果均显示，SIRT3过表达可增强线粒体生物发生，并逆转ccRCC中的线粒体功能障碍。研究发现，SIRT3可通过调控转录因子A（TFAM）的转录、降解及乙酰化水平提升其活性：SIRT3过表达后，TFAM K154位点的乙酰化水平降低，而TFAM蛋白表达量升高。进一步研究表明，SIRT3可与TFAM结合，降低其乙酰化修饰水平，进而促进TFAM在线粒体生物发生过程中的活性。综上，本研究揭示了SIRT3调控线粒体功能的全新机制：ccRCC中SIRT3的下调会降低TFAM的活性，继而抑制线粒体基因转录与线粒体生物发生。